This project will examine the visual systems of four mutants of the mouse that were discovered to be visually defective. The goal of the project is to find out where in the visual system each mutant gene exerts its effect. The analysis to date has shown that one of these mutants has abnormally low sensitivity of the retina in the dark-adapted condition. However, the electroretinogram is normal. The next step will be to localize further the affected site by recording from the isolated retina and by applying anatomical techniques. In addition, these mutants, though able to produce vestibularly-induced eye movements, do not have optokinetic nystagmus. The possibility that the primary targets of the retinal ganglion cells are incorrectly innervated will be investigated by autoradiographic techniques.